The long term goal of the proposed research is to gain a detailed understanding of the regulation of SOS and heat-shock networks in Escherichia coli. One portion of the research will be concerned with an analysis of the newly-isolated css mutations which affect proteolysis and the regulation of the heat-shock response. The css gene(s) will be cloned and their gene products identified, the relationship of the css gene(s) to cellular protease activities will be investigated, the mechanism by which css mutations affect the heat-shock response will be determined, and the regulation of the css gene(s) themselves will be explored. Another portion of the research will be devoted to an analysis of aspects of the regulation of the heat-shock response. This work will include the use of operon and gene fusions to isolate new regulatory mutants and a systematic investigation of properties of the dnaK gene product. Finally, we will continue to analyze the regulation and function of a number of genes that are members of the SOS regulatory network. The studies should offer insights into the interactions between these two global regulatory networks and into the role of proteolytic degradation in cellular regulatory processes. The E. coli SOS and heat-shock regulatory networks are useful as models for regulatory networks induced by DNA damage and stress in more complex organisms.